MEMS Fabry Perot Filter for Integrated Spectroscopy System

ABSTRACT

Integrated spectroscopy systems are disclosed. In some examples, integrated tunable detectors, using one or multiple Fabry-Perot tunable filters, are provided. Other examples use integrated tunable sources. The tunable source combines one or multiple diodes, such as superluminescent light emitting diodes (SLED), and a Fabry Perot tunable filter or etalon. The advantages associated with the use of the tunable etalon are that it can be small, relatively low power consumption device. For example, newer microelectrical mechanical system (MEMS) implementations of these devices make them the size of a chip. This increases their robustness and also their performance. In some examples, an isolator, amplifier, and/or reference system is further provided integrated.

RELATED APPLICATIONS

This application is a Division of U.S. application Ser. No. 10/688,690filed on Oct. 17, 2003, which is incorporated herein by reference in itentirety.

BACKGROUND OF THE INVENTION

Minimally, optical spectroscopy systems typically comprise a source forilluminating a target, such as a material sample, and a detector fordetecting the light from the target. Further, some mechanism is requiredthat enables the resolution of the spectrum of the light from target.This functionality is typically provided by a spectrally dispersiveelement.

One strategy uses a combination of a broadband source, detector array,and grating dispersive element. The broadband source illuminates thetarget in the spectral scan band, and the signal from the target isspatially dispersed using the grating, and then detected by an array ofdetectors.

The use of the grating, however, requires that the spectroscopy systemdesigner make tradeoffs. In order to increase the spectral resolution ofthese systems, aperturing has to be applied to the light provided to thegrating. As more spectral resolution is required, more light is requiredto be rejected by the narrowing spatial filter. This problem makes thisstrategy inappropriate for applications requiring a high degree ofspectral precision combined with sensitivity.

Another approach is to use a tunable narrowband source and a simpledetector. A typical approach relies on a tunable laser, which is scannedover the scan band. By monitoring the magnitude of the tunable laser'ssignal at the detector, the spectrum of the sample is resolved. Thesesystems have typically been complex and often had limited wavelengthscanning ranges, however.

Still another approach uses light emitting diodes (LEDs) and anacousto-optic modulator (AOM) tunable filter. One specific examplecombines multiple light emitting diodes (LEDs) in an array, each LEDoperating at a different wavelength. This yields a relatively uniformspectrum over a relatively large scan band. The light from the diodes isthen sent through the AOM tunable filter, in order to create the tunableoptical signal.

The advantage of this system is the use of the robust LED array. Thisprovides advantages over previous systems that used other broadbandsources, such as incandescent lamps, which had limited operatinglifetimes and high power consumption.

While representing an advance over the previous technology, thedisadvantages associated with this prior art system were related to theuse of the AOMs, which are relatively large devices with concomitantlylarge power consumptions. Moreover, AOMs can also be highly temperaturesensitive and prone to resonances that distort or alter the spectralbehavior, since they combine a crystal with a radio frequency source,which establishes the standing wave in the crystal material to effectthe spectral filtering.

Grating-based spectrometers also tend to be large devices. The devicepackages must accommodate the spatially dispersed signal from thesample. Further, the interface between the grating and the detectorarray must also be highly mechanically stable. Moreover, these gratingbased systems can be expensive because of costs associated with thedetector arrays or slow if mechanical scanning of the detector orgrating is used.

SUMMARY OF THE INVENTION

The drawbacks associated with the prior art spectrometers arise from thelarge size of the devices combined with the high cost to manufacturethese devices combined with poor mechanical stability. These factorslimit the deployment of spectrometers to applications that can justifythe investment required to purchase these devices and furtheraccommodate their physical size.

Accordingly, the present invention is directed to an integratedspectrometer system. Specifically, it is directed to the integration ofa tunable Fabry-Perot system with a source system and/or detectorsystem. The use of the Fabry-Perot filter system allows for a highperformance, low cost device. The integration of the filter system withthe source system and/or detector system results in a device with asmall footprint. Further, in the preferred embodiment, the filter systemis based on microelectromechancial systems (MEMS), which yield a highlymechanically robust system.

In general, according to one aspect, the invention features aspectroscopy system. The system comprises a source system for generatinglight to illuminate a target, such as a fiber grating or a materialsample. A tunable Fabry-Perot filter system is provided for filteringlight generated by the source. A detector system is provided fordetecting light filtered by the tunable filter from the target.According to the invention, at least two of the source system, tunableFabry-Perot filter system, and the detector system are integratedtogether.

Specifically, in one embodiment, the source system and tunableFabry-Perot system are integrated together on a common substrate, suchas an optical bench, also sometimes called a submount. In anotherembodiment, the tunable Fabry-Perot filter system and the detectorsystem are integrated together on a common substrate, such as an opticalbench. Finally, in still another implementation, all three of the sourcesystem, tunable Fabry-Perot filter system, and the detector system areintegrated together on a common bench, and possibly even in a commonhermetic package.

Temperature control is preferably provided for the system. Currentlythis is provided by a heater, which holds the temperature of the systemabove an ambient temperature, or a thermoelectric cooler. For example,the thermoelectric cooler is located between the bench and the packageto control the temperature of the source system, tunable Fabry-Perotfilter system, and/or the detector system. As a result, a single cooleris used to control the temperature of the filter and SLED chip, loweringpower consumption, decreasing size, while increasing stability.

In the preferred embodiment, the source system comprises a broadbandsource. This can be implemented using multiple, spectrally multiplexeddiode chips. Preferably, superluminescent light-emitting diodes (SLEDs)are used. These devices have a number of advantages relative to othersources, such incandescent sources. Specifically, they have betterspectral brightness, longer operating lifetimes, and a smaller formfactor.

In order to increase the spectral accuracy of the system, a tap can alsobe used to direct a part of the tunable signal to a detector. A spectralreference, such as a fixed etalon with multiple spectral transmissionpeaks is placed between the detector and the tap, in order to create afringe pattern on the detector during the scan, thereby enablingmonitoring of the wavelength of the tunable signal. An optical power tapcan also be included to monitor the real time emitted optical powerduring the scan.

The tunable Fabry-Perot filter system comprises single or multiplefilters. In one example, multiple serial filters are used. In anotherembodiment, multiple parallel filters are used.

In still further embodiments, multiple detectors can be used. Thesedetectors can be responsive to different wavelengths or a calibrationsignal.

In the preferred embodiment, in order to make the system small, compactand highly robust, a micro-electro-mechanical system (MEMS) Fabry-Perottunable filter is used. These devices can achieve high spectralresolutions in a very small footprint.

Finally, in the preferred embodiment, isolation is provided between thesource system and the tunable Fabry-Perot filter system. This preventsback reflections from the filter into the source system that can disturbthe operation of the source system. In one example, an isolator isinstalled on the optical bench between the SLED and the tunable filter.A quarter wave plate can also be used. This rotates the polarization ofthe returning light so that it is not amplified by the highlypolarization anisotropic SLED gain medium. In another embodiment, theisolation is provided on the bench, with the tunable Fabry-Perot filtersystem and the detector system.

The present invention is also directed to an integrated tunable sourcethat combines a broadband source and a tunable filter, such as a tunableFabry-Perot filter, although other tunable filters could be used in thisconfiguration. Applications for this device extend beyond spectroscopy.

Between the tunable filter and the light source, isolation is preferablyprovided. This stops back reflections from the tunable filter into thediode, which could impact its performance. Isolation can be achievedusing a number of techniques. In one embodiment, a discrete isolator isused. In another embodiment, when a SLED is used as the source, aquarterwave plate is used between the SLED chip and the filter. Finally,a flat-flat cavity Fabry-Perot tunable filter is used in still anotherembodiment, with isolation being accomplished by tilting the filterrelative to the SLED.

A variety of other light sources can be used, including LEDs, dopedfiber or waveguide amplified spontaneous emission sources, and thermalsources.

According to still another aspect, the invention features a high powertunable source. This addresses one of the primary drawbacks associatedwith the use of a broadband source and tunable filter configuration,namely their usually low output power. Specifically, an opticalamplifier is further added in order to increase the power of the tunablesignal. As a result, power levels comparable to those attainable withtunable lasers can be achieved in this configuration.

In a typical implementation, the amplifier is a semiconductor opticalamplifier (SOA). In other examples, various types of fiber amplifiersare used, however.

The above and other features of the invention including various noveldetails of construction and combinations of parts, and other advantages,will now be more particularly described with reference to theaccompanying drawings and pointed out in the claims. It will beunderstood that the particular method and device embodying the inventionare shown by way of illustration and not as a limitation of theinvention. The principles and features of this invention may be employedin various and numerous embodiments without departing from the scope ofthe invention.

The above and other features of the invention including various noveldetails of construction and combinations of parts, and other advantages,will now be more particularly described with reference to theaccompanying drawings and pointed out in the claims. It will beunderstood that the particular method and device embodying the inventionare shown by way of illustration and not as a limitation of theinvention. The principles and features of this invention may be employedin various and numerous embodiments without departing from the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, reference characters refer to the sameparts throughout the different views. The drawings are not necessarilyto scale; emphasis has instead been placed upon illustrating theprinciples of the invention. Of the drawings:

FIGS. 1A and 1B illustrate embodiments of the integrated spectroscopysystem according to the present invention;

FIG. 2 is a perspective view showing a tunable source, according to thepresent invention, and including a detector system for detecting thetunable signal from the sample;

FIG. 3A is a perspective view of the MEMS Fabry Perot tunable filter,used in embodiments of the present invention, which is compatible withtombstone mounting on the optical bench;

FIG. 3B is an exploded view of the inventive Fabry Perot tunable filter;

FIG. 4 is a perspective view showing an amplified tunable source,according to the present invention, in a hermetic package;

FIG. 5 is a perspective view showing a reference detector embodiment ofa tunable source, according to the present invention, in a hermeticpackage;

FIG. 6 is a block diagram of an embodiment of the tunable source withboth a wavelength and power reference detector;

FIG. 7 is a perspective view showing still another embodiment of atunable source, according to the present invention, using two SLEDchips;

FIG. 8 is a perspective view showing a further embodiment of a tunablesource, according to the present invention using multiple SLED chips andtunable filters;

FIG. 9 is a perspective view showing another embodiment of a tunablesource, according to the present invention, using parallel filters andmultiple SLED sources;

FIG. 10 is a perspective view showing a further embodiment of a tunablesource, according to the present invention, using serial filters;

FIG. 11 is a plot of wavelength as a function of transmission showingthe relationship between the free spectral ranges of the serial filters,in one embodiment;

FIG. 12A is a perspective view of a tunable detector spectroscopysystem, according to the present invention;

FIG. 12B is a perspective view of another embodiment of a tunabledetector spectroscopy system, according to the present invention;

FIG. 13 is a perspective view of still another embodiment of a tunabledetector spectroscopy system, according to the present invention, usingmultiple parallel filters; and

FIGS. 14 and 15 show two fully integrated spectroscopy systems in whicha tunable source and a detector system are integrated on the same bench.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A and 1B illustrate an integrated spectroscopy system 1, whichhas been constructed according to the principles of the presentinvention.

Specifically, FIG. 1A shows two alternative integration configurations.

According to configuration 1, a source system 100 is provided. This is abroadband source, which generates light 40 for illuminating a target,such as sample S-1 or a fiber grating, for example. This targetselectively absorbs and/or scatters the light from the source system100. The transmitted light is then received by a tunable Fabry-Perotfilter system 200. This functions as a narrow band tunable spectralfilter. It tunes its passband over the scan band within the spectralband of the source system 100. As a result, it resolves the spectrum ofthe target S-1 into a time response. This time-resolved signal is thendetected by detector system 300.

According to the integration provided by this configuration 1, thetunable Fabry-Perot filter system 200 and the detector system 300 areintegrated together. Specifically, in the preferred embodiment, thetunable Fabry-Perot filter system 200 and the detector system 300 areinstalled on a common bench B-1. Moreover, in the current embodiment,the tunable Fabry-Perot filter system 200 and the detector system 300are integrated together on the common bench B-1 in a common hermeticpackage.

The integration of the Fabry-Perot filter system 200, with the detectorsystem 300 on the common bench B-1, yields the tunable detector 20 whichis characteristic of the configuration 1 integration.

FIG. 1A also illustrates a second configuration, configuration 2integration. In this second configuration, the source system 100 and thetunable Fabry-Perot system 200 are integrated together. In the preferredembodiment, they are installed together on a common bench B-2. Further,in the current implementation, the source system 100 and the tunableFabry-Perot filter system are integrated together on the common benchB-2 and installed in a common hermetic package to yield a tunable source10. This tunable source 10 generates a tunable signal 30, which is usedto illuminate a target, located in this second configuration at positionS-2. The target either scatters or absorbs spectral components of thetunable signal as it is scanned across the scan band. This allows thedetector system 300 to resolve the time varying signal as the spectralresponse of the target S-2.

FIG. 1B illustrates a fully integrated system according to still anotherembodiment. Here, the source system 100, the tunable Fabry-Perot filtersystem 200, and the detector system 300 are integrated together.Specifically, in the preferred embodiment, they are integrated togetherand installed on a common bench B. This bench B is preferably located ina hermetic package.

Depending on whether the tunable source system 100, the Fabry-Perotfilter system 200, and detector system 300, are combined as a tunablesource 10 or tunable detector 20, the target is located either inposition S-1 or S-2. Specifically, in the implementation of a tunablesource 10 with the source system 100 and the tunable Fabry-Perot filtersystem 200 functioning to create a tunable signal, the tunable signal 30is coupled outside of the hermetic package and off of the bench B to thetarget S-2, in the case of configuration 2. Alternatively, if thetunable Fabry-Perot filter system 200 and the detector system 300function to yield the tunable detector 20, then the broadband signal 40from the source system 100 is coupled off of the bench and the outsideof the hermetic package to the target S-1 in the case of the firstconfiguration.

FIG. 2 illustrates a first embodiment of the tunable source 10.Specifically, in this embodiment, the bench B-2 holds the tunableFabry-Perot filter system 200 and the source system 100 on a commonplanar surface. The generated tunable signal 30 is coupled off of thebench B-2 by an optical fiber 102. In the preferred embodiment, thisoptical fiber 102 is a single transverse mode fiber. This has advantagesin that it renders the tunable signal 30 very stable, even in the eventof mechanical shock to the single mode fiber 102.

The source system 100 is implemented using, in this embodiment, asuperluminescent light emitting diode (SLED) 110. The diode 110 isinstalled on a submount 112. The submount 112 is, in turn, installed onthe bench B-2. In the preferred embodiment, the SLED chip 110 is solderbonded to the submount 112, which further includes metallizations 114 tofacilitate wire bonding to provide electrical power to the SLED chip110. Further, the submount 112 is solder bonded to the bench B-2, whichin turn, has metallizations 115 to enable formation of the solder bonds.

These SLEDs are relatively new, commercially-available devices and aresold by Covega Corporation, for example, (product numbers SLED 1003,1005, 1006). These devices are currently available in wavelength rangesfrom 1,200 nanometers (nm) to 1,700 nm from a variety of vendors. Theyare waveguide chip devices with long gain mediums similar tosemiconductor optical amplifiers. An important characteristic is theirhigh spectral brightness.

The broadband signal 40 that is generated by the SLED chip is collimatedby a first lens component 114. This lens component 114 comprises a lenssubstrate 117, which is mounted onto a deformable mounting structure118. The deformable mounting structure is preferably as those structuresdescribed in U.S. Pat. No. 6,559,464 B1 to Flanders, et al., which isincorporated herein in its entirety by this reference. The alignmentstructure system allows for post installation alignment by mechanicaldeformation of the mounting structure 118 of the lens substrate 117.

The collimated light from the first lens component 114 in the preferredembodiment is coupled through an isolation system, such as an isolator120 or quarterwave plate. The beam from the isolator is then collimatedby a second lens element 122 and coupled into the Fabry-Perot tunablefilter system 200. The isolator system prevents all back reflections orback reflections that have a polarization that is aligned with the gainpolarization of the SLED chip 110. These reflections arise from theFabry-Perot filter system 200. This isolation promotes the stability inthe operation of the SLED chip 110.

In the preferred embodiment, the tunable filter system 200 isimplemented as a MEMS tunable Fabry-Perot filter 116. This allows forsingle transverse mode spectral filtering of the broadband light 40 fromthe SLED chip 110, yielding the tunable signal 30. Tunable signal 30 iscoupled into the endface 104 of the single mode optical fiber 102. Inthe current embodiment, the endface 104 of the optical fiber 102 is heldin alignment with the MEMS tunable filter 116, via a fiber mountingstructure 106. Again, this allows for post installation alignment of thefiber endface 104 to maximize coupling of the tunable signal 30, intothe single mode fiber 102. The fiber 102 transmits the tunable signal 30to target S-2 and then, the response is detected by detector system 300.

Depending on the embodiment, the Fabry-Perot filter 116 has either acurved-flat cavity or a flat-flat cavity. The curved flat cavityincreases angular tolerance between the two mirrors of the Fabry-Perotfilter. The flat-flat cavity provides better single mode operation.Moreover, there is the option to avoid the necessity for discreteisolators or waveplates by angle isolating the filter for the sourcesystem 100.

FIG. 3A is a close up view of the tunable filter 116. The tunable filter116 comprises a MEMS die 410. This has a number of wire bond locations412 for making electrical connection to the MEMS die 410. A MEMS die 410provides the moveable mirror portion or component of the tunable filter.A fixed mirror portion or component 414 is bonded to the MEMS die 410 inorder to define the Fabry Perot cavity. In one embodiment, the fixedmirror component provides the flat mirror and the MEMS die 410 providesthe curved mirror.

In the preferred embodiment, the tunable filter 116 is “tombstone”mounted onto the bench B, B-1, B-2. Specifically, the fixed mirrorsubstrate 414 extends down below the bottom of the MEMS die 416 by adistance L. Specifically, the fixed mirror substrate has a bottomsurface 418 that serves as a foot that is bonded to the bench.Preferably, a layer of solder 420 is used to attach the fixed mirrorsubstrate 414 to the bench B. In the preferred embodiment, the distanceL is approximately 1-10 micrometers.

FIG. 3B is an exploded view of the tunable filter 116. This shows thefixed mirror substrate 414 disconnected from the MEMS die 410. Flexures421 define a MEMS membrane 423. The deflectable membrane 423 holds themirror layer 424 of the tunable mirror and covers a depression 425formed in the membrane 423 that forms the curved mirror of oneembodiment. Metallization pads 426 are provided on the MEMS die 410 inorder to solder attach the fixed mirror substrate 414 to the MEMS die410.

The general construction of this tunable filter is described in, forexample, U.S. patent application Ser. No. 09/734,420, filed on Dec. 11,2000 (now Publication No. U.S. 2002-0018385). This application isincorporated herein, in its entirety by this reference.

FIG. 4 illustrates another embodiment of the tunable source 10. In thisembodiment, the broadband signal generated by the SLED chip 110 is againcoupled through a first lens component 114 to an isolator 120. A secondlens component 122 is further provided for coupling the broadband signalinto the filter 116 of the Fabry-Perot filter system 200.

Then, a third lens component 126 is provided to couple the tunableoptical signal 30 into a semiconductor optical amplifier 128. In thepreferred embodiment, this semiconductor optical amplifier chip 128 isinstalled on an amplifier sub-mount 130, which is installed on the benchB-2. The amplified tunable optical signal generated by the semiconductoroptical amplifier chip 128 is then coupled into the endface 104 of theoptical fiber 102 to be coupled out of the hermetic package 132. Thisallows the tunable signal 30 to be coupled, in an amplified state, tothe target S-2 followed by detection by the detector system 300.

In some other embodiments additional isolators are located between thefiber endface 104 and the amplifier chip 128 and between the amplifierchip 128 and the third lens component 126.

In the preferred embodiment, the hermetic package 132 is a standardtelecommunications hermetic package. Specifically, it comprises astandard butterfly package. The lid 136 is shown cut away to illustratethe internal components. Further, the optical bench B-2 is preferablyinstalled on a thermoelectric cooler 134, which enables a controlledenvironmental temperature to stabilize the operation of the SLED chip110 and the tunable Fabry-Perot filter system 200.

Electrical leads 138 are further provided to transmit electrical signalsto the pads 146 on the inside of the hermetic package 132. Wire bond aremade between pads 146 and the active components such as the SLED chip110, MEMS tunable filter 116, and SOA 128.

The FIG. 4 embodiment has the advantage that the tunable signal 30received from the tunable Fabry-Perot filter system 200 is amplified tofurther increase the dynamic range and the signal-to-noise ratio of thespectroscopy system.

In the embodiment of FIG. 5, the tunable source 10 also combines a SLEDchip 110, a first lens component 114, isolator 120, and a second lenscomponent 122. This launches the broadband signal 40 from the SLED chipinto the tunable filter system 200. A third lens component 126 isfurther provided. This collimates the beam. A splitter, however,comprising a partially reflective substrate 149, provides a portion ofthe tunable signal 30 to a detector 140. This detector 140 can be usedto monitor the magnitude or power in the tunable signal 30. In anotherembodiment, a reference substrate 148 is installed between the detector140 and the tap 149. This reference substrate 148 provides stablespectral features. In one embodiment, this is provided by a fixed etalonsubstrate. A controller monitoring the output of the detector 140compares the tunable signal to the spectral features of the referencesubstrate 148 to thereby resolve the instantaneous wavelength of thetunable signal 30.

In still other embodiments, instead of a reference substrate, a gas cellis used as the spectral reference for calibrating the scan of thetunable filter 116. Also two splitters can be included to providesimultaneous spectral and power references.

The tunable signal, which is not coupled to the detector 140 by the tap149 is launched by a fourth lens component 147 into the fiber endface104 of the optical fiber 102.

FIG. 6 illustrates the general operation provided by a controller 150 ofthe tunable source 10. Specifically, the controller 150 is used tocontrol the power or current supplied to the SLED chip 110. Itsbroadband signal 40 is coupled to the isolator 120. The controller alsocontrols the tunable pass band of the tunable filter system 200 togenerate the tunable signal 30.

In the case of monitoring the frequency of the tunable signal, a firsttap 149 couples a portion of the tunable signal to a spectral reference148, which in the illustrated embodiment, is a fixed etalon. This allowsthe detector 140 to detect the wavelength of the tunable signal 30during the scan.

In the preferred embodiment, a power detector 154 is also provided. Thisis added to the optical train using second tap 152, which again couplesthe portion of the tunable signal 30 to a power detector 154. Thecontroller 150 controls and monitors the wavelength detector 140 and thepower detector 154 to determine both the wavelength and the power in thetunable signal 30.

FIG. 7 illustrates another embodiment of the tunable source 10. Thisembodiment is used either to increase the power or the spectral width ofthe scan band of the tunable source 10. Specifically, multiple SLEDchips, and specifically two SLED chips 110A and 110B, are installedtogether on the optical bench B-2. In the illustrated embodiment, theSLED chips 110A and 10B are installed on a common sub-mount 112, whichis in turn, bonded to the bench B-2.

Two first lens components 118A, 118B are provided to couple thebroadband signals from their respective SLED chips 110A, 110B andcollimate those beams. A combination of a fold mirror 156 and a combiner158 are provided to combine the broadband signals from each of theseSLED chips 110A, 110B into a single broadband signal, which is coupledthrough the isolator 120.

The beam from the isolator 120 is then focused by a second lenscomponent 122 into the tunable filter 200. A third lens component 126then couples the tunable signal into the optical fiber 102 via theendface 104.

In the high power version of the FIG. 7 embodiment, a polarizationrotator, such as a quarterwave plate 160 is provided in the beam path ofone of the SLED chips 110A, 110B. In the illustrated embodiment, thispolarization rotator 160 is provided in the beam path of the second SLEDchip 110. This rotates the polarization of the light from the secondSLED chip 110B by 90°. Then, the combiner 158 is a polarization combinerthat is transmissive to the polarization of the light from the firstSLED chip 110A, but reflective to the polarization of light from thesecond SLED chip 110B. As a result, the beams from each of the SLEDchips 110A, 110B are merged into a common broadband signal withincreased power.

In a second implementation of the FIG. 7 embodiment, the SLED chips110A, 110B operate at different spectral bands. Specifically, SLED chip110A generates light in a scan band A and SLED chip 110B generates lightin an adjacent but different scan band B. The combiner 158 is awavelength division multiplex combiner that is configured to betransmissive to the band of light generated by the SLED chip 110A, butreflective to light in the band generated by SLED chip 110B. As aresult, the combined signal generated together by the SLED chip 110A,110B has a broader scanband then could be generated by each of the SLEDchips individually. This allows for increased bandwidth in the tunablesignal 30 that is generated by the tunable source 10.

FIG. 8 illustrates another embodiment of the tunable source 10. Thisembodiment uses a tunable filter system 200, which includes an array oftunable filters 116 and broadband light sources in order to increase thespectral width of the scanband. Typically, and in the illustratedembodiment, an array of five SLED chips 110 are mounted in common on thebench B-2. The light from each of these SLED chips 110 is collimated byrespective first lens components 118. Specifically, there is a separatelens component 118 for each of these SLED chips 110. Separate isolators120 are then provided for the broadband signals from each of the SLEDchips 110.

An array of second lens components 122 is further provided to couple thebroadband signal into an array of tunable filters 200. Specifically,separate Fabry-Perot tunable filters 116 are used to filter the signalfrom each of the respective SLED chips 110. Finally, an array of thirdlens components 126 is used to re-collimate the beam from the tunableFabry-Perot filters 116 of the tunable filter system 200.

For channel 1, C-1, a fold mirror 156 is used to redirect the beam fromthe SLED chip 110. The WDM filter 160 is used to combine the broadbandsignal from the SLED chip 110 of channel C-2 with the signal fromchannel C-1. Specifically, the filter 160 is reflective to thewavelength range generated by the SLED chip 110 of channel C-2, buttransmissive to the wavelength range of light generated by the SLED chip110 of channel C-1.

In a similar vein, WDM filter 162 is reflective to the signal bandgenerated by the SLED chip 110 of channel C-3, but transmissive to thebands generated by SLED chips 110 of channels C-1 and C-2. WDM filter164 is reflective to the light generated by SLED chip 110 of channelC-4, but transmissive to the bands generated by the SLED chips 110 ofchannels C-1, C-2, and C-3. Finally, WDM filter 158 is reflective to allof the SLED chips, but the SLED chip 110 of channel C-5. As a result,the light from the array of SLED chips is combined into a single broadband tunable signal 30.

A first tap 149 is provided to reflect a portion of the light throughthe etalon 148 to be detected by the wavelength detector 140. Then,another portion is reflected by tap 152 to the power detector 154. Theremaining tunable signal is coupled by the fourth lens component 106into the optical fiber 102 via the endface 104.

The FIG. 8 embodiment can operate according to a number of differentmodes via a controller 150. Specifically, in one example, only one ofthe SLED chips in channels C-1 to C-5 is operating at any given momentin time. As a result, the tunable signal 30 has only a single spectralpeak. The full scan band is achieved by sequentially energizing the SLEDchip of each channel C-1 to C-5. This tunable signal is scanned over theentire scan band covered by the SLED chips of channels C-1 to C-5turning on the SLED chips in series, or sequentially.

In another mode, each of the SLED chips is operated simultaneously. As aresult, the tunable signal has spectral peaks in each of the scan bands,covered by each of the SLED chips 110 simultaneously. This systemresults in a more complex detector system 300, which must demultiplexthe separate scan bands from each of the SLED chips 110 from each of thechannels at the detector. Specifically, in one embodiment, five (5)detectors are used with a front-end wavelength demultiplexor.

FIG. 9 shows an embodiment of the tunable source 10 that has bothincreased power and increased scanning range over a single SLED. Itcomprises two subcomponents, which are configured as illustrated in FIG.7 embodiment. Specifically, each channel C-1, C-2 has two SLED chips110A, 110B that are polarization combined. The output is isolated by anisolator 120 and then filtered by a tunable filter 116 for each channelC-1, C-2. The signals from the two channels are then wavelengthmultiplexed using a combination of a fold mirror 170 and a dichroic orWDM filter 172. Specifically, the dichroic mirror 172 is transmissive tothe scan band of the SLED chips 110A, 110B of channel C-1, butreflective to the SLED chips 110A, 110B of channel C-2.

In order to improve the manufacturing yield of the FIG. 9 embodiment, inone implementation, each of the channels C-1 and C-2 are fabricated onseparate sub-benches SB-1 and SB-2. The sub-benches SB-1, SB-2 are thenbonded to each other or to a common bench in order to yield the FIG. 9embodiment.

FIG. 10 illustrates still another embodiment, which covers a widespectral band. Specifically, it includes five SLED chips 110A to 110E. Aseries of first lens optical components 118 are used to collimate thebeams from each of the SLED chips 110A-110E. In the present embodiment,the SLED chips 110A to 110E, each operate over different spectral bands.They are then wavelength combined using a combination of fold mirrorsand filters 156, 160, 162, 164 and 158, as discussed with reference tothe FIG. 8 embodiment.

The FIG. 10 embodiment further includes, preferably, two isolators 120A,120B. These isolate respective tunable filters 116A, 116B. Lenscomponents 180, 182, 184, and 186 are used to couple the optical signalgenerated by the SLEDS 110A-110E, through the first tunable filter 116Aand the second tunable filter 116B of the tunable filter system 200, andthen, through the wavelength tap 149 and the power tap 152 to theendface 104 of the optical fiber 102.

The use of the five SLED chips 110 increases the effective scan band ofthe tunable source 10. In the preferred embodiment, the tandem tunablefilters have free spectral ranges FSR as illustrated in FIG. 11.

Specifically, filter 1 116A, and filter 2 116B have different freespectral ranges. As a result, they function in a vernier configuration.This addresses limitations in the free spectral range of the tunablefilters individually.

Typically, if a single tunable filter was used, its free spectral rangewould have to be at least as wide as the total scan band of the broadband signals generated by the sources. In the illustrated embodiment,the tunable filters are combined to increase the free spectral range ofthe tunable filter system, since the peak transmissivity, through bothtunable filters 116A-116B, only arises at wavelengths where thepassbands of the two filters 116A-166B are coincident.

FIGS. 12A and 12B show tunable detector systems 20, to which theprinciples of the present invention are also applicable.

Specifically, with reference to FIG. 12A, the tunable detector systemgenerally comprises a package 132 and an optical bench B-1, which issometimes referred to as a submount. The bench B-1 is installed in thepackage 132, and specifically on a thermoelectric (TE) cooler 134, whichis located between the bench B-1 and the package 132, in the specificillustrated embodiment.

The package 132, in this illustrated example, is a butterfly package.The package's lid 136 is shown cut-away in the illustration.

The tunable detector optical system, which is installed on the topsurface of the bench B-1, generally comprises the detector system 300,the tunable filter system 200, and an optional reference source system24.

In more detail, the optical signal from the target S-1 to be monitoredis transmitted to the system via a fiber pigtail 310, in the illustratedexample. This pigtail 310 terminates at an endface 312 that is securedabove the bench B-1 using a fiber mounting structure 314 in theillustrated implementation. The optical signal passes through a firstlens optical component 316, which collimates the beam to pass through anisolator 320. A second lens optical component 318 launches the opticalsignal into the tunable filter system 200. A MEMS implementation of thetunable filter is shown. The filtered signal passes through a third lensoptical component 322 and is then detected by an optical signal detector324.

In the illustrated implementation, each of the lens and tunable filteroptical components comprises the optical element and a mountingstructure that is used to secure the optical element to the bench, whileenabling most installation alignment.

Turning to the path of the optical reference, the emission from areference light source 42, such as a broadband source, e.g., a SLED,passes through reference lens optical component 44 to a fixed filter 46,which, in the present implementation, is a fixed etalon. It converts thebroadband spectrum of the SLED 42 into a series of spectral peaks,corresponding to the various orders of the etalon transmission, therebyproducing the stable spectral features of the optical reference.

The optical reference is then reflected by fold mirror 48 to a dichroicor WDM filter 50, which is tuned to be reflective at the wavelength ofthe optical reference, but transmissive within the band of the opticalsignal. Thus, the optical reference is similarly directed to the opticalfilter system 200.

At the detector system 20, a dichroic filter 52 reflects the opticalreference to a reference detector 54.

FIG. 12B shows an operationally similar tunable optical filter system20, for the purposes of the present invention. Reference numerals havebeen used for functionally equivalent parts. The differential betweenthe two designs lies in the design of the detector system 300. Thissecond embodiment utilizes only a single detector 324, 54 that detectsboth the optical reference and the optical signal. In this illustration,the package is not shown for clarity.

FIG. 13 shows another embodiment of the tunable detector 20. The signalfrom the target is transmitted to the detector 20 via fiber 310. A firstlens component 316 collimates the light from the fiber. Second lenscomponents 318 couple the light into the tunable filters 116A, 116B ofthe filter system 200. Third lens components 322 focus the light to thedetector system 300.

This version uses two tunable filters 116A, 116B, each filtering aportion of the scan band. Corresponding detectors 334A, 334B detect thetransmitted signal from each filter.

The spectrum is divided into two subbands by WDM filter 360, whichreflects half of the spectral scan band to the second filter 116B viafold mirror 362. The other half of the spectrum is transmitted throughthe WDM filter 360 to tunable filter 116A.

FIG. 14 shows a single bench fully integrated system according to stillanother embodiment. It generally operates as described relative to theFIG. 8 embodiment. Specifically, it uses a series of SLEDs in fivechannels, yielding a tunable source 10, to generate a wide band tunablesignal 30. The detector system 300 is integrated on the same bench B andthe tunable source. Specifically, light returning from the target infiber 310 is coupled to detector 334 using lens component 322.

FIG. 15 shows another single bench fully integrated system according tostill another embodiment. Here, the light to and from the target iscarried in the same fiber 102, 310. The tap substrate 152 is used todirect outgoing light 30 to the power detector 154 and light returningfrom the target to the detector 334.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A MEMS Fabry Perot filter system comprising a filter including a MEMStunable movable mirror die and a fixed mirror substrate, which is bondedto the MEMS mirror die, wherein the filter is edge bonded onto anoptical bench.
 2. A MEMS tunable filter system as claimed in claim 1,wherein the fixed mirror substrate extends below a bottom of the MEMSmirror die for attachment to the optical bench
 3. A MEMS tunable filtersystem as claimed in claim 1, wherein the MEMS mirror die is separatedfrom the optical bench and supported by the fixed mirror substrate.
 4. AMEMS tunable filter system as claimed in claim 1, further comprising anedge emitting semiconductor source chip bonded to the optical bench theoptical emission from the chip being directed through the filter.
 5. AMEMS tunable filter system as claimed in claim 4, wherein the sourcechip comprises an semiconductor optical amplifier.
 6. A MEMS tunablefilter system as claimed in claim 4, further comprising a a detectorsystem for detecting the light filtered by the filter from a sample,wherein the detector system is integrated on the bench with the sourcechip and the filter.